1. Field of the Invention
The present invention generally relates to steelmaking and, more particularly, is concerned with a pneumatic steelmaking vessel and a method for the production of steel from hot carbon-bearing raw materials such as Direct Reduced Iron (hereinafter "DRI").
2. Description of the Prior Art
The invention encompasses a pneumatic steelmaking vessel and a method for the production of steel from hot carbon-bearing raw materials such as DRI. The vessel is substantially a ladle having an eccentric top with an opening on one side. Opposite the opening in the top is at least one downwardly directed oxygen lance or tuyere. The vessel is mounted on trunnions for rotation about its central axis to a generally horizontal position. The bottom of the vessel has a porous plug, and a hot metal outlet controlled by a sliding gate closure member or other convenient type closure. The vessel is used in connection with a method of steelmaking by serving as the means for transporting molten metal to melting, refining, ladle metallurgy, and teeming operations.
There are several significant advantages that the invention provides over other melting, refining, ladle metallurgy and teeming systems in current commercial operation.
First, metal is melted and refined in the same vessel as is used to transport the molten metal to subsequent operations. In current practice, the metal is melted and refined in a separate furnace such as an electric arc furnace, basic oxygen furnace, energy optimizing furnace, induction furnace or other known device and then tapped from this device into a ladle for transport. Not having to transfer the molten metal into a ladle for transport has significant advantages over the current practice. There is a substantial temperature loss occasioned in current practice because even a preheated receiving ladle is almost always cooler than the molten steel and extracts heat until the differing temperatures equalize. A second temperature loss occurs in current practice due to the exposure of the molten stream to the atmosphere during the transfer operation. This is analogous to cooling a cup of hot liquid by pouring it back and forth between two cups.
Second, oxidation of non-metallics in the molten steel will occur by exposure of the metal stream to atmospheric oxygen during the transfer operation. These non-metallic oxides become inclusions in the final product, lowering its overall quality. Of paramount importance to the production of high quality clean steel is minimal contact with the atmosphere.
Third, in current practice, transfer ladles are fitted with removable covers during transport to minimize temperature losses by radiation through a normally open ladle. The present vessel is equipped with an integral top that performs this same function without having to be fitted and removed at various stations.
Fourth, under current practices, repair or relining of the melting furnace requires a complete shutdown of the melting functions associated with that furnace until the work is completed. The invented vessel can be repaired off-line and a repaired vessel inserted in its place with no loss of production.
Fifth, the invented vessel has an integral yet removable top into which is fitted at least one tuyere. Since most refractory wear is associated with the area immediately adjacent to the tuyeres due to the action of the injected gases, a vessel can be removed from service and fitted with a rebuilt (or relined) top section without the necessity of relining the entire vessel with new refractory. It is anticipated that each vessel will be refitted with several rebuilt (or relined) top sections before it becomes necessary to replace the refractory lining in the vessel body.
Sixth, because the top section is removable from the body of the vessel, refractory replacement in either section is simplified. Both are basically conical sections and adaptable to automatic ladle lining by the use of ramming machines. Rammed monolithic linings are preferred over laid-upon brick linings for their lower cost and potentially longer life.
Seventh, the use of hot DRI pellets contributes to the thermal efficiency that makes the invented method possible without external energy sources. Hot DRI pellets can only be obtained from a facility located immediately adjacent to the steelmaking facility. The technology described in Holley U.S. Pat. No. 3,836,353, entitled "PELLET RECLAMATION PROCESS," makes such an arrangement feasible.
Eighth, the use of hot DRI pellets containing a least 2% carbon eliminates the need for the complicated addition of carbon into the vessel by injection tuyeres or other similar devices. It also eliminates the need to provide the crushing, storage and transport systems needed to inject carbon. Again, the Holley process is capable of producing hot DRI pellets containing at least 2% carbon, which is not possible with other direct reduction processes currently in operation.
The applicants are aware of the following U.S. patents concerning related metallurgical methods and apparatus.
__________________________________________________________________________ U.S. Pat. No. Issue Date Inventor Title __________________________________________________________________________ 253,046 Jan. 31, 1882 HENDERSON BESSEMER-STEEL PLANT 3,746,325 Jul. 17, 1973 FREEBERG, et al BASIC OXYGEN STEEL MAKING FACILITY AND METHOD OF OXYGEN REFINING OF STEEL 429,337 June 3, 1890 COLLIN CONVERTER LADLE 3,502,313 Mar. 24, 1970 PASTORIUS STEEL PRODUCING PLANT WITH UMBILICALLY OPERATIVE FURNACE TOP MEANS 3,484,088 Dec. 16, 1969 PERE MULTI-CONVERTING PNEUMATIC STEELMAKING PLANT 3,477,705 Nov. 11, 1969 MOBLEY STEEL MAKING APPARATUS 3,411,764 Feb. 17, 1966 FALK STEELMAKING PLANT HAVING A MOBILE, STRADDLE CARRIAGE CONVERTER SUPPORT 3,013,789 Dec. 17, 1959 SAYRE, et al MOBILE APPARATUS FOR OXYGEN REFINING OF METAL 2,803,450 Sept. 29, 1953 McFEATERS CONVERTER GAS CLEANING SYSTEM 741,505 Oct. 13, 1903 KIRK MELTING FURNACE 51,401 Dec. 5, 1865 BESSEMER IMPROVEMENT IN THE MANUFACTURE OF MALLEABLE IRON AND STEEL 2,065,691 Jul. 8, 1933 HANSON, et al CUPEL FURNACE 574,127 Dec. 29, 1896 AIKEN HOISTING APPARATUS __________________________________________________________________________
Henderson illustrates a trunnion-mounted Bessemer converter for making steel, which is mobile and moveable along beams.
Freeberg illustrates a basic oxygen steelmaking facility which includes mobile furnaces that may be moved along tracks. According to this patent "this arrangement makes possible an operation in which each of the two furnaces are charged in succession, blown with oxygen in succession, and thereafter tapped and recycled, so that one conventional blowing station can serve each of the furnaces while the preblowing and postblowing operations are carried out elsewhere."
Collin shows a rail-mounted, hot-metal ladle which is charged with molten metal from a furnace while in the upright position and blown when inclined or horizontal. The tuyeres are generally centered in the ladle cover, and the taphole in the ladle cover apparently also acts as the charging hole.
Pastorius allegedly shows and illustrates "a steel producing plant providing a consecutive series of stations for standby, loading, preheating, blowing, degassing, blocking, pouring, or discharge with a carriage supporting a refractory line steel producing vessel to move through the consecutive series of stations for the melting and refinement of steel." Each operation is conducted at a separate location. It is also alleged that "the vessel becomes in effect a ladle after the steel is properly made and may then pass to a second holding station to determine if the additives properly reacted." The vessel is top blown with oxygen, and the blowing station has a removable cover. The vessel is moved without a cover or hood.
Pere illustrates a multi-converter pneumatic steelmaking plant in which the top blown converters are arranged in carrousel formation.
Mobley illustrates steelmaking apparatus for oxygen refining of steel utilizing a succession of movable furnaces moveable along a track way. Each furnace has a flue at each end for communication with the flue of an adjacent furnace. An oxygen lance is included in the roof of each furnace for top blowing.
Falk illustrates a steelmaking plant having a mobile carriage-mounted converter, which may also be used for alloying operations.
Sayre illustrates a track-mounted hot metal car which operates as a mobile furnace apparatus for use in oxygen refining of steel.
McFeaters teaches a rail mounted converter with an off-set mouth, as best shown in his FIG. 6, which is mounted for rotation about trunnions for charging, blowing, and discharging or dumping. The converter has a top blown oxygen lance.
Kirk shows a trunnion-mounted unitary bottom-blown vessel, with a similar configuration to a Bessemer converter.
Bessemer illustrates that bottom-blown steelmaking vessels have been known since at least 1865.
Neither Hanson U.S. Pat. No. 2,065,691 nor Aiken U.S. Pat. No. 574,127 presents any material which is strongly applicable to the subject invention.
Each of the prior art references cited above suffer from the disadvantages of low thermal efficiency, and other disadvantages previously discussed. Applicants are unaware of any prior art steelmaking vessel that accomplishes the objects of the present invention. Consequently, a need exists for a pneumatic steelmaking vessel and a method for the production of steel from hot carbon-bearing raw materials such as DRI which will result in improved steelmaking.